are u referring to retail album tracks getting remastered by the recording companies? if so, then remastering of a track usually involves cleaning it up to remove clicks, hissing, etc. occasionally they’ll also re-record the music if the original isn’t up to their standards. i’ve even seen a few remastered tracks get remixed.

It’s supposed to mean that the original multi-track studio master tape is used to re-mix and re-master the recording to a stereo PCM master. What “enhancements” are applied would depend on the quality of the original and the intent of the engineer.
There is no “standard” for these things, it’s mostly a marketing ploy and may not mean anything at all.